1. Field of the Invention
This invention relates to a semiconductor device and, more particularly, it relates to a method of forming a contact hole for electrically connecting a lower electroconductive film and an upper electroconductive film arranged with an insulation film interposed therebetween. The present invention also relates to a liquid crystal apparatus such as a display apparatus using such devices.
2. Related Background Art
In recent years, display apparatus have been playing ever-increasing important roles as means of multi-media communication using images, sounds and written texts. Of them, liquid crystal display apparatus have the advantage of being very thin and consuming little power and the industry of manufacturing liquid crystal display apparatus has grown to a major industry that is comparable with the semiconductor manufacturing industry. It is expected that liquid crystal display apparatus are used in the future not only for personal computers but also for work stations and home television sets having a large display screen. However, a large liquid crystal display apparatus having a large screen is accompanied by high manufacturing cost and electric requirements to be met to drive its large screen. Normally, the manufacturing cost of a liquid crystal display apparatus increases as a function of the square to the cube of the size of the display screen.
In an attempt to bypass this problem, projection systems adapted to optically enlarge the image formed on a relatively small liquid crystal display screen for viewing have been attracting attention. Such a system has become feasible due to the recent technological development that has made it possible to manufacture high-performance micro-semiconductor devices on a mass production basis to exploit the scale merit.
Recently, reflection type liquid crystal panels realized by forming an active matrix circuit including peripheral drive circuits on a semiconductor substrate and comprising pixel electrodes for driving liquid crystal that operate also as reflectors for reflecting light have been attracting attention from the viewpoint of low cost and high image quality.
FIG. 23 of the accompanying drawings is a partial cross sectional view of a known reflection type liquid crystal panel.
Referring to FIG. 23, it shows a semiconductor substrate 1, p-type wells 2, n-type wells 2xe2x80x2, transistor source regions 3, 3xe2x80x2, transistor gate regions 4, transistor drain regions 5, 5xe2x80x2, a filed oxide film 6, a shield layer 7, insulation layers 8, 8xe2x80x2, an insulation layer 9, source electrodes 10, drain electrodes 11, pixel electrodes 12, an anti-reflection film 13, a liquid crystal material 14, a common transparent electrode 15, an opposite electrode 16, high concentration impurity layers 17, 17xe2x80x2, a Pxe2x80x94SiO layer, a display region 19, an anti-reflection film 20, an insulation layer 21, a seal member 22, a through hole 23, a matrix substrate (for semiconductor devices) 24, a Pxe2x80x94SiO layer 18-1 and an SOG layer 18-2.
In the final stage of preparing the matrix substrate (for semiconductor devices) 24 of a reflection type liquid crystal panel as illustrated in FIG. 23, the pixel electrodes 12 are separated from each other by the insulation film 9 and, at the same time, the surfaces are smoothed and polished by CMP (chemical mechanical polishing) as the pixel electrodes 12 also operate as reflectors.
However, as shown, the through hole 23 leaves its vestige in the form of a recess on the corresponding pixel electrode 12 after the CMP operation so that light is reflected by the recess not perfectly as desired but irregularly to reduce the brightness and the contrast of the displayed images.
Such recesses may be produced by an insufficiently buried pixel electrode film and then the yield of manufacturing liquid crystal panels can be reduced due to defective electric conductivity of through holes.
While a round-etching technique is known to enlarge the size of the through hole at the top thereof to avoid the problem of an insufficiently buried pixel electrode, the technique involves a number of additional steps and large cost.
On the other hand, with a reflow technique using metal such as aluminum and high temperature sputtering to utilize the metal as pixel electrode, the metal film should be made very thick in order to completely bury the through hole 23. Then, the time required for depositing the metal film and polishing the film by CMP is enormous to remarkably raise the overall cost of manufacturing a semiconductor device if compared with conventional manufacturing methods.
Therefore, it is an object of the present invention to provide a semiconductor device comprising a contact hole for connecting electroconductive films having a stepped profile with the top having a size greater than the bottom, the top size of the contact hole being defined in a self-aligning manner by another film disposed between said electroconductive films.
Another object of the invention is to provide a method of manufacturing a semiconductor device having a semiconductor substrate, a principal electrode mounted on the substrate and a contact hole, characterized in that said method comprises steps of:
(1) forming a coat of a first insulation film on the surface of the substrate;
(2) forming a coat of a first electroconductive film and patterning it to a desired profile;
(3) forming a coat of a second insulation film and patterning it to a desired profile, said first insulation film being simultaneously processed in a self-aligning manner relative to the patterned profile of said first electroconductive film within the region produced by removing said first electroconductive film in step (2) and located within the region being removed of the second insulation film;
(4) forming a coat of a third insulation film and forming a contact hole connected to said principal electrode of the semiconductor device within the region of said first insulation film processed in a self-aligning manner relative to the patterned profile of said first electroconductive film in said step (3); and
(5) forming a coat of a second electroconductive film and patterning it to a desired profile;
to make the size of the contact hole change stepwise.
Preferably, said first insulation film has a multilayer structure including an SOG (spin on glass) layer.
Preferably, a semiconductor device according to the invention is used for a liquid crystal apparatus comprising a plurality of pixel electrodes arranged to form an active matrix and provided with respective switching devices and liquid crystal held between said pixel electrodes and a common electrode disposed vis-a-vis semiconductor devices.